The statements in this section merely provide background necessary to understand the invention and may not be prior art.
Petroleum has been the primary source of transportation fuels for the last century and continues to heavily dominate the market today. Many economic, political and environmental factors contribute to the desire for alternatives to petroleum for the essential transportation fuels. Various alternative fuels are being examined, but almost all require substantial modifications or additions to the current infrastructure.
Examples of fuels considered include alcohols such as methanol and ethanol, but they require both vehicle modifications and a new distribution infrastructure as they are corrosive to existing infrastructure. Examples of other fuels considered include CNG (compressed natural gas) and LNG (liquified natural gas), but these require even more extensive engine modifications, bulky and expensive fuel tanks, and complete changes to the refueling infrastructure. Other fuels considered include higher alcohols such as butanol but they have a lower energy density than gasoline.
For 40 years, a process of converting methanol to gasoline (MTG) has been known. This process would allow for production of a gasoline fuel that requires no major infrastructure modifications while allowing for a larger and more flexible resource base. Since methanol can be produced from a huge variety of sources including natural gas, coal, and biomass, it is an attractive process but has yet to see significant applications due to the relatively low cost of petroleum products.
Unfortunately, the MTG process requires multiple steps, including first transforming methanol to dimethyl ether, then transforming dimethyl ether to propylene, and finally transforming propylene to gasoline. This multi-stage system adds complexity and cost to the MTG process. As a result, the MTG process is not economically attractive, except when oil prices are extremely high. Thus, there is a need to develop an economic means for conversion of methanol to gasoline.
Ethanol is a major product used as a fuel and chemical produced both from renewable and petroleum and natural gas feed stocks. The ethanol to gasoline (ETG) process requires multiple steps, first transforming ethanol to diethyl ether, then transforming diethyl ether to ethylene, and finally transforming ethylene to gasoline. This multistage system adds complexity and cost to the ETG process. Additionally, ethanol from fermentation sources is difficult to fully purify as the dehydration process cannot be completed with simple distillation. As a result the ETG process is not economically attractive, except when oil prices are extremely high. Thus there is a need to develop an economic means for conversion of ethanol to gasoline.
Due to the parity in the MTG and ETG processes, it is possible to combine the two alcohols in any ratio and still achieve highly efficient conversion to gasoline. The ability to freely mix alcohols allows for a wide range of potential alcohol sources. Water can also be mixed with the ethanol feed, and while it may be thermodynamically unfavorable it is still possible to achieve efficient conversion. The tolerance of water in the feed could allow for drastically reduced ethanol costs since the ethanol could be utilized before undergoing several costly distillation and drying steps.
The present invention allows for high-efficiency conversion of ethanol, mixtures of ethanol and methanol, or mixtures of methanol and ethanol and water to aromatic compounds usable as gasoline in one step, in one pass, within a single mixed catalyst reactor. Such a system allows for radically lower plant costs since fewer independent reactors, condensers, valves, pipes, pumps, transducers, and control system elements are used, and combining catalysts leads to higher one-pass conversions and a reduction in the total material required. The fuels produced from this system are high energy products that are readily compatible with the existing transportation fuel infrastructure.
Therefore, it would be an advancement in the state of the art to provide a system and method for converting methanol and/or ethanol and/or mixtures thereof to gasoline-type aromatic hydrocarbons (hereinafter referred to as “gasoline”).
It is against this background that various embodiments of the present invention were developed.